Michael Cera is the Peter Pan of the millennial generation: at 22, he seems stuck in preadolescence, his appearance nearly the same as it was in his early TV roles and in starring stints in Superbad, Nick & Norah's Infinite Playlist and Youth in Revolt. His voice hasn't changed yet, and his only facial hair is his eyebrows. What was the name of his breakout TV show in 2003? Ah, yes: Arrested Development. (See the 100 best movies of all time.)

Even when playing someone his own age  the hero of Scott Pilgrim vs. the World  Cera seems like the movies' coolest, most reticent tween. A Toronto layabout who plays in the not-so-hot rock band Sex Bob-omb, Scott shares a bed but nothing more with his gay roommate Wallace (Kieran Culkin); has an intensely platonic relationship with a high school girl, Knives Chau (Ellen Wong); and on the night he finds true love with dream girl Ramona Flowers (Mary Elizabeth Winstead), spends it with her but doesn't have sex. A lot of us would like to be half our ages, but if a guy is 22, he maybe doesn't want to be 11.

Then again, since so many action movies play out kids' video-game fantasies of blowing stuff up, and since guy comedies trade largely in school-yard taunts and boys'-room giggles, maybe Cera's wise-child stasis makes him the current ideal of a young star. If so, then Scott Pilgrim is the perfect summation of Hollywood at this moment  an apotheosis of American male infantilism  and, on its own, a most likable mess. (See more about Scott Pilgrim at Techland.com.)

Very closely adapted from the first of Bryan Lee O'Malley's six Scott Pilgrim comic books, the film was directed by Edgar Wright, the Englishman who sublimely mashed genres in Shaun of the Dead (rom-com meets zombie movie) and Hot Fuzz (a quirky cop comedy that flares into a splatter fest). So he's just the gent to take on a love story that's also a martial-arts showdown: in order to win Ramona's hand, Scott must do battle, video-game style, with her seven evil exes.

Pow! Zap! Thud!If you're a fan of narrative integrity, stay away. The first half of the movie is an acutely observed character comedy, as we meet the women in Scott's life: Knives; Ramona; the band's drummer, Kim (Alison Pill); and Scott's sister Stacey (Anna Kendrick), all of whom are worthier humans than he. Then the fights begin, people sprout superhero powers at whim, and comic-book visual effects  lightning bolts, heart-shaped kisses, whooshes and thuds  accompany the action as in the old Batman TV show.

This section can get wearying if you're not Scott's emotional age. But Wright leaves a residue of sweetness from the first part, in which the perpetually immature Scott has to choose among all those fabulous women. That's what makes Scott Pilgrim a fizzy, defiantly schizophrenic semidelight.